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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Hund's rule

In a set of degenerate orbitals (the three pp or five dd), electrons go into separate orbitals with parallel spins before any orbital gets a second electron. This keeps electrons apart and minimizes their repulsion.

Nitrogen: three 2p2p electrons, one per orbital, all parallel.

Example

Carbon's 2p22p^2 is (↑)(↑)( ), with 2 unpaired electrons, not (↑↓)( )( ). Manganese's 3d53d^5 has all five electrons unpaired.

See alsoDegenerateUnpaired electronOrbital diagramPauli exclusion principle